1. Technical Field
The present invention relates to a resistive film type input device which is capable of detecting one or a plurality of locations touched by a finger, a pen, or the like, a display device with an input function which includes the resistive film type input device, and an electronic apparatus which includes the display device with the input function.
2. Related Art
As an electronic apparatus such as a cellular phone, a car navigation, a personal computer, a ticket vending machine, or a bank terminal, recently, there has been known an electronic apparatus in which an input device called a touch panel is disposed on the surface of a liquid crystal device and information is input with reference to an image displayed on an image display area of the liquid crystal device. In a resistive film type input device among the input devices, a first planar resistive film 16 and a second planar resistive film 26 are generally formed on the surfaces of a first insulating substrate 10 and a second insulating substrate 20 opposed to each other, respectively, as shown in FIG. 9A. With such a configuration, when the second insulating substrate 20 is pressed down at a predetermined location, the first planar resistive film 16 and the second planar resistive film 26 partially come in contact with each other. Therefore, when a voltage in a Y direction is applied to the first planar resistive film 16 through first strip-shaped feeding electrodes 17a and 17b and a potential Vsy is detected through the second planar resistive film 26, the contact location in the Y direction can be detected. When a voltage in an X direction is applied to the second planar resistive film 26 through second strip-shaped feeding electrodes 27a and 27b and a potential Vsx is detected through the first planar resistive film 16, as shown in FIG. 9B, the contact location in the X direction can be detected.
This resistive film type input device has an advantage in that information can be input with a pen differently from a capacitance type input device. However, this resistive film type input device has a defect in that exact detection cannot be achieved. That is because when two locations are simultaneously pressed down, resistances from the contact locations are combined to each other and detected.
In order to solve this defect, as shown in FIGS. 10A and 10B, there was suggested a resistive film type input device in which a planar resistive film 18 and strip-shaped feeding electrodes 19a and 19b which apply a voltage to both the ends in an X direction of the planar resistive film 18 are formed in a first insulating substrate 10 and a plurality of strip-shaped resistive films 28a, 28b, . . . , and 28f extending in the X direction are arranged in parallel in an Y direction in a second insulating substrate 20 (see JP-A-2001-34419).
In this resistive film type input device, when a voltage V1 is applied to the planar resistive film 18 through the feeding electrodes 19a and 19b and a constant potential V2 is sequentially applied to one end portions 281a, 281b, . . . , and 281f of the plurality of strip-shaped resistive films 28a, 28b, . . . , and 28f, the potentials of the other end portions 282a, 282b, . . . , and 282f of the plurality of strip-shaped resistive films 28a, 28b, . . . , and 28f are sequentially detected. In this resistive film type input device, when the first insulating substrate 10 or the second insulating substrate 20 is pressed down and the planar resistive film 18 comes in contact with the strip-shaped resistive films 28a, 28b, . . . , and 28f, the contact locations cause a variation in resistant values of contact locations contacted to the other end portions 282a, 282b, . . . , and 282f of the strip-shaped resistive films 28a, 28b, . . . , and 28f. Accordingly, since the potentials detected from the other end portions 282a, 282b, . . . , and 282f of the plurality of strip-shaped resistive films 28a, 28b, . . . , and 28f vary, the positions in the X direction of the contact locations can be detected. Moreover, the plurality of strip-shaped resistive films 28a, 28b, . . . , and 28f are arranged in parallel in the Y direction, the positions in the Y direction of the contact locations can be detected. Even when the first insulating substrate 10 or the second insulating substrate 20 is simultaneously pressed at two different locations in the Y direction, it is possible to specify the two pressed locations.
However, a resistance deviation easily occurs since the resistive film is formed of an ITO film or the like having a thin thickness. Accordingly, in the configuration disclosed in JP-A-2001-34419, it is necessary to form resistive films in both the first insulating substrate 10 and the second insulating substrate 20. For this reason, a problem occurs in that detection precision deterioration caused due to the resistance deviation of the resistive films easily occurs. Moreover, in the configuration disclosed in JP-A-2001-34419, since the resistance values of the strip-shaped resistive films 28a, 28b, . . . , and 28f are required to be larger than that of the planar resistive film 18 by one or two digits, it is necessary for the film thickness of the respective strip-shaped resistive films 28a, 28b, . . . , and 28f to be considerably thin. Accordingly, since the resistance deviation easily occurs in the strip-shaped resistive films 28a, 28b, . . . , and 28f, a problem occurs in that the detection precision deterioration easily occurs. Moreover, in the configuration disclosed in JP-A-2001-34419, the voltage is applied to the strip-shaped resistive films 28a, 28b, . . . , and 28f of the second insulating substrate 20 as well as the planar resistive film 18 of the first insulating substrate 10 and the potential is also detected on the side of the second insulating substrate 20. Accordingly, a problem occurs in that the configuration is complicated.